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Programming-Idioms

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Idiom #85 Check if integer addition will overflow

Write boolean function addingWillOverflow which takes two integers x, y and return true if (x+y) overflows.

An overflow may be above the max positive value, or below the min negative value.

import core.checkedint;
bool addingWillOverflow(int x, int y)
{
    bool result;
    core.checkedint.adds(x, y, result);
    return result;
}
function Adding_Will_Overflow (X, Y : Integer) return Boolean is
begin
   return X > 0 and Y > 0 and X > Integer'Last - Y;
end Adding_Will_Overflow;

PROBLEM: this doesn't detect negative overflow.

New implementation...
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